Exploring the production of bio-succinic acid from apple pomace using an environmental approach

Highlights

• Based on lab data, the LCA of BioSA at industrial scale is modelled.

• LCA was applied to assess the environmental profile.

• The results highlight hotspots in the production process.

• Distillation unit to solvents recovery plays a key role.

• Recommendations are given to improve the environmental profile and production process.

Abstract

Fermentation-derived bio-succinic acid (BioSA) is a valuable intermediate; it is used as a chemical building block, and has multiple industrial applications as an alternative to petroleum counterparts. The aim of this study was to develop a full-scale plant to produce BioSA from apple pomace, a low-cost solid waste from the cider- and juice-making industry, based on a biorefinery concept, and to determine its environmental profile using a cradle-to-factory-gate, scaled-up LCA approach. Foreground data used in this LCA were based on mass and energy flows, modelled in detail. The production process was divided into three stages: i) reconditioning and storage; ii) fermentation with Actinobacillus succinogenes; and iii) purification. The results indicate that the use of enzymes is responsible for the highest environmental burdens, due to their highly energy-intensive background production processes. When these were excluded from the analysis (following other studies available in the literature), the purification stage played an environmentally significant role, due to the extraction and distillation units involved. The electricity use and the requirements for organic solvents in these operations make up the largest environmental burdens. Thus, approaches with the highest potential for improvement must involve both operations. Alternatives for improvement are proposed that offer interesting potential reductions in the environmental profile, especially at the purification stage.

Introduction

Today, both society and industry are facing important challenges regarding the use of biomass and the production of bio-based materials, in relation to social responsibility and environmental concerns. Hence, the substitution of petroleum-based materials by their bio-based counterparts is a key factor in the battle against climate change [1].

Bio-based products have been promoted as part of sustainable consumption strategies, and are obtained from the integration of eco-innovation approaches aimed at reducing greenhouse gas (GHG) emissions and combating the depletion of fossil sources [2]. New environmental regulations and economic considerations also support this interest in renewable sources [3]. Bio-based materials (e.g. wood, paper and textile products) and synthetic ones produced from fossil feedstocks account for 14% and 7%, respectively, of the global production of bulk materials [4]. Thus, the interest in substituting biomass sources for fossil feedstocks within the production of synthetic materials has increased in recent years, with the aim of guaranteeing the security of the supply of industrial feedstocks.

Biomass is an available resource abundant in the nature, and is diverse and recyclable; it has multiple applications either as a clean source of renewable energy or as a raw material for the production of biomaterials and biochemicals [3], [5]. Concerns regarding competition with the food and feed sectors at a global level have encouraged the utilisation of biomass waste as a potential feedstock. In view of this, the valorisation of biomass residues is receiving attention, and its use is expected to increase in the future, mainly in emerging technologies in the production of second generation biofuels and in the recovery of high-added-value products [6].

The general assumption that bio-based materials are environmentally superior to fossil-based ones requires detailed analysis. In order to guarantee improvements in the environmental profile of bio-based products, it is mandatory to perform a life cycle assessment (LCA)-based study, since the term “bio-based” is not always synonymous with “environmentally friendly” [2], particularly in terms of less well-known impact categories such as eutrophication, acidification, water depletion [4], [5] and land use. Hence, if dedicated biomass is valorised, the cultivation activities related with biomaterial feedstock production play an important role, especially in areas of significant social value [7]. A sustainability study is therefore required to identify situations in which the use of bioresources over petrochemical ones is environmentally feasible.

The introduction of the biorefinery concept and the challenge of integrating bio-based chemicals are key issues generating attention to the valorisation of waste in the industrial sector. In 2004, the US Department of Energy identified the most important chemicals that could be obtained from biorefinery carbohydrates [8]. One of these chemicals was succinic acid (C₄H₆O₄) (or butanedioic acid), which is a promising renewable platform chemical, mostly due to its functionality and the value of its derivatives [9]. There is extensive recent literature focused on its production and use as chemical building block [5], [10], [11], [12]. Succinic acid is a precursor of several well-known petrochemical products such as 1,4-butanediol, tetrahydrofuran, γ-butyrolactone and polybutylene succinates, among others. Moreover, succinic acid has multiple industrial applications in biodegradable polymers (polyesters, polyamides and polyesteramides), foods (e.g. as an acidulant, flavorant and sweetener), fine chemicals and pharmaceuticals [13], [14]. However, it has been commonly considered a niche product, primarily due to its high price [14]. Currently, it is mainly produced from n-butane/butadiene by a chemical process via maleic anhydride, using the C4 fraction of naphtha [14]. The global market has been predicted to grow by around 19% annually between the years 2011 and 2016 [5]. However, the price fluctuations of petroleum-based counterparts and environmental concerns have motivated an interest in the production of BioSA [5], [13], [14]. It can be obtained from the biological transformation of biorefinery sugars (via the bacterial fermentation of carbohydrates), from a variety of feedstocks and using multiple microorganisms [15]. Moreover, carbon dioxide is needed by these microorganisms for BioSA production, as carbon dioxide fixation is involved in the reductive TCA cycle, and this can provide environmental benefits such as the reduction of greenhouse gas emissions [13], [14]. Several companies (e.g. BioAmber and Mitsui & Co) are therefore working on the commercialisation of BioSA [5]. Currently, this represents less than 5% of total succinic acid production [5].

As previously indicated, multiple types of biomass sources can be used for the production of BioSA through microbial fermentation [12]. The most frequently used carbon sources in industrial fermentation are purified sugars and glucose syrup from corn [13]. However, the use of agricultural and food residues and industrial side streams have interesting results, primarily from a sustainability perspective. Of these, apple pomace is a potential feedstock; this is the main solid waste produced in cider and apple juice factories [16], and can add up to as much as 35% of the total processed raw material. Apple pomace is a term for the solid residues, which consist of a mixture of skin, pulp and seeds derived from the production of concentrated apple juice, jam and sweets [17]. Since they are highly biodegradable, the disposal of these wastes represents an interesting environmental problem involving several challenges. Although apple pomace is used as a feed component (a low added value use) and in pectin production, this use requires only 20% of the total production, and the remaining 80% is sent to landfill [17]. Thus, numerous studies have been performed with the aim of identifying other potential applications [16]. The production of high added value products such as lactic acid, oligosaccharides [18], citric acid, antioxidants, dietary fibers and even biopolymers (chitosan and xanthan gum) have received particular attention [17].

In this study, an assessment is performed of the environmental impacts arising from the valorisation of apple pomace from the cider industry into BioSA by microbial fermentation; this follows the LCA methodology and uses a cradle-to-factory-gate approach. To our knowledge, there are only two peer-review studies that analyse the environmental impacts of BioSA [5], [11], and these examine alternative feedstocks (such as glucose from corn or sorghum). In the following, a large-scale system for BioSA is described in detail, and particular attention is paid to the design process.